668
FXUS63 KARX 252355
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
655 PM CDT Wed Sep 25 2024

.KEY MESSAGES...

- Trending drier through the weekend. Highs in the 70s to low
  80s are forecast for the end of September, with signal for a
  potential cool down sometime early next week.

&&

.DISCUSSION...
Issued at 309 PM CDT Wed Sep 25 2024

No significant changes as a fairly quiet forecast remains on track.
Clear skies, light low level flow, and longer nights will keep
valley/river valley fog the main forecast concern in the short term.
Have continued to mention valley fog for tonight/Thursday morning
and will continue to watch the subtle details for further
potential and day to day impacts through the rest of the week.
Otherwise, ensemble solutions look to be in better agreement on
the overall pattern as a closed upper level low settles
generally over the Mid-South region and Helene moves inland and
eventually gets absorbed by the low. As has been noted with the
past couple of forecasts, there has been a trend towards a drier
forecast heading into the weekend, with highest precipitation
probabilities in both the GEFS and ECMWF remaining just
southeast of the forecast area. Have noted a handful of ECMWF
and GEFS ensemble members hinting towards low probabilities
(<30%) reaching towards far southwestern WI late in the weekend,
so will continue to monitor trends over the next couple of
days. Overall though, have maintained the drier forecast.
Otherwise, forecast high temperatures remain in the 70s to
around/low 80s.

Heading into early next week model guidance shows an upper level
trough and associated cold front moving through the region. Still a
bit of spread between ensemble solutions in regards to precipitation
potential and temperatures. However, there does appear to be signal
for a cooling trend back down to more normal/below normal
temperatures.

&&

.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 655 PM CDT Wed Sep 25 2024

Valley fog will be the primary TAF consideration with an overall
favorable environment given reasonably favorable dewpoint
depressions (20F at KLSE as of 25.23z), clear skies and light
wind layer in the recent RAP soundings to around 5kft. The main
questions with this forecast throughout the next 6-12 hours will
revolve around any mid-level clouds that can develop and how
favorably dewpoint depressions will trend for the rest of the
evening to suggest if 1/4SM will be possible at KLSE. Looking at
recent model soundings, very slight saturation can be noted
around 850mb above the nighttime inversion. As a result, would
not be able completely rule out some cloud cover at this level,
although this appears very unlikely (5-10% chance) given the
fairly large temperature/dewpoint spread. Otherwise, high
confidence remains that valley fog will occur at KLSE early
Thursday morning. Consequently, have maintained the 1/2SM to
account for this. Will need to monitor how dewpoints trend over
the next 6 hours to determine if a tempo 1/4SM will need to be
introduced for the 26.06z issuance but opted not to include it
at this time.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.

&&

$$

DISCUSSION...EMS
AVIATION...Naylor